The proposed research includes studies of microneurosurgical anatomy and cerebral microvascular surgery. MICRONEUROSURGICAL ANATOMY: The rapid growth of microneurosurgery (clinical neurosurgery done using 3-40X magnification) has created a need for studies of microsurgical anatomy. The original grant, of which this is a continuation, began in 1970 and was entitled "Brain Stem Sensory Connections." The original studies in animals suggested that microanatomic studies in man would be rewarding and upon renewal of this grant, a major section of it was related to microsurgical anatomy. Subsequent studies led to significant new anatomic findings of importance to the neurosurgeon. These studies will be extended to the perforating arteries of the Circle of Willis important in aneurysm surgery, pineal region, ventricular system, pituitary gland, the portion of the cranial base involved in cerebrospinal fluid leaks, intra and extracranial arteries forming the basis for cerebral microvascular surgery, and the extracranial branches of the facial nerve. MICROVASCULAR SURGERY: The original grant led into studies of the effect of neural stimulation on cortical blood flow. Microsurgical technique, by permitting surgical anastomosis of vessels less than 1 mm in diameter, has stimulated a neurosurgical interest in cerebral vascular disease and especially those cases not amenable to conventional macrosurgical techniques. More recently, we completed a microvascular study comparing blood flow through arterial and vein grafts to the occluded basilar artery of the dog. In the proposed study, graft blood flow will be measured in arterial and vein grafts to the occluded middle cerebral artery using electromagnetic technique and cerebral blood flow in the brain distal to the graft will be measured using the hydrogen clearance technique.